Acid gas scrubbing composition

ABSTRACT

This invention provides novel compositions comprising substituted polyamines as acid gas scrubbing solutions and methods of using the compositions in an industrial system. The invention relates to the use of such polyamine compounds in industrial processes to remove acidic contaminants from natural and industrial fluid streams, such as natural gas, combustion gas, natural gas, synthesis gas, biogas, and other industrial fluid streams. The compositions and methods of the invention are useful for removal, absorption, or sequestration of acidic contaminants and sulfide contaminants including CO 2 , H 2 S, RSH, CS 2 , COS, and SO 2 .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/397,131, filed on Feb. 15, 2012, which is a divisional ofU.S. patent application Ser. No. 12/494,521, filed on Jun. 30, 2009, nowU.S. Pat. No. 8,461,335, the contents of each of which are incorporatedherein fully by reference.

TECHNICAL FIELD

This invention relates generally to the use of novel compounds as acidgas scrubbing solutions. More specifically, the invention relates to theuse of substituted heterocyclic amines and polyamine compounds inindustrial processes to remove acidic contaminants from natural andindustrial fluid streams, such as natural gas, combustion gas, syntheticgas streams, and hydrocarbon fluids. The invention has particularrelevance to processes for removal of carbon dioxide from gas streamshaving sour gas impurities.

BACKGROUND

Natural gas is a mixture of gaseous hydrocarbons and non-hydrocarbonimpurities and contaminants. Removal of, for example, carbon dioxide andacidic sulfide contaminants (e.g., CO₂, H₂S, RSH, CS₂, COS, SO₂, etc.)to meet quality and regulatory requirements in natural gas that is fedinto distribution pipelines is a major industrial burden. Suchcontaminants are often corrosive and may also impair the caloric valueof the gas. In addition, increasing concerns of global warming from CO₂and other emissions has prompted significant investments into methods ofcapturing such contaminants more efficiently and economically.

Aqueous solutions of commonly available commodity alkanolamines aregenerally used as scrubbing solutions (chemical absorbents) in gasprocessing. The purpose of these scrubbing systems is to remove acidiccontaminants from the raw gas stream. As energy sources are beingdepleted and environmental restrictions are tightening, the economic useof the “bottom of the barrel” in gasification processes is increasing.There are many new projects being sanctioned, most of which would needacid gas clean-up to remove contaminants during processing. Removing CO₂from flue gases is also important for a variety of reasons, such as asecondary CO₂ market, enhanced oil recovery, and greenhouse gasreduction.

Weak organic bases, such as monoethanolamine (MEA), diethanolamine(DEA), and methyldiethanolamine (MDEA) comprise many of the typicalalkanolamine solvents known in the art. MDEA is known to have advantagesfor CO₂ removal and other acid gas contaminants in high-pressure gasstreams. The amount of energy required to regenerate the MDEA is lowbecause it is a relatively weak base and therefore the chemical bondformed during the reaction with CO₂ is weaker than with other commonlyused alkanolamines A secondary benefit lies in the nature of thechemical bond formed during absorption. As a tertiary alkanolamine, MDEAreacts with CO₂ to form a bicarbonate ion rather than a carbamate, whichresults in a reaction ratio MDEA to CO₂ of 1:1. In contrast, othercommonly used primary and secondary alkanolamines preferentially form acarbamate and require a reaction ratio of 2:1. The reaction between CO₂and tertiary alkanolamines (e.g., MDEA) is typically of a greaterefficiency than between CO₂ and other commonly used primary andsecondary alkanolamines. These combined benefits result in a process ofgreater efficiency and capacity than is possible with commercial primaryand secondary alkanolamines such as MEA and DEA.

A disadvantage of using tertiary alkanolamines is that CO₂ is indirectlyabsorbed, resulting in a weak driving force and slow rate of reactioncompared to other commercial alkanolamines. In high-pressure gascontacting systems the effect of the weak driving force is minimized dueto the higher fraction of CO₂ that can be achieved in the liquidresulting from the high CO₂ partial pressure in the gas above it. Whengasses are contacted at low pressure, the driving force is weak as thepartial pressure of CO₂ is also weak. Thus, there is no beneficialeffect of pressure, and the CO₂ equilibrium established between the gasand liquid is low. Tertiary alkanolamines are not normally used inlow-pressure applications because of their low equilibrium loading.Other more commonly used primary and secondary amines such as MEA andDEA, which are stronger bases, are used in these applications due totheir higher driving force and increased rate of reaction with CO₂. Inthese low-pressure situations, the disadvantage of the inefficientcarbamate reaction is outweighed by the greater equilibrium liquiddistribution achieved.

In an effort to increase the capacity of MDEA for CO₂ at low partialpressure, a number of improvements to the basic MDEA process have beendeveloped. These improvements typically involve the addition of smallamounts of primary or secondary amines to the MDEA solution (asdescribed in U.S. Pat. Nos. 5,209,914 and 5,366,709 and PCT ApplicationNo. WO 03/013699). The resulting mixtures are commonly described asformulated or blended MDEA with additives referred to as “catalysts,”“absorption accelerators,” or “activators” (e.g., U.S. Pat. No.6,740,230). These additives generally function by increasing the rate ofCO₂ absorption into the MDEA blend solution at low CO₂ partial pressurethereby increasing the fraction of CO₂ in the liquid as compared to theMDEA solution alone.

Although effective in the removal of CO₂ as described, the commercialapplication of known formulated solvents has less than ideal operatingcharacteristics. Some of the additives used for formulating have limitedsolubility in MDEA, which reduces their effectiveness, and theircommonly lower boiling (some are not lower) points in turn createdifficulties in maintaining their concentration. Moreover, the reactionproducts of the additives with CO₂ are also problematic. As they arestronger organic bases than MDEA these blends have a tendency to requiremore energy for regeneration and their products have limited solubility.Such characteristics limit their effectiveness and the efficiency of theoverall process if their concentration exceeds approximately 20% of thetotal amine in solution.

There thus exists an industrial need for improved compositions andmethods for recovering acidic contaminants from both high and lowpressure systems. A particular need exists for products having thebenefits of both low-pressure equilibrium capacity of primary orsecondary amines and the efficiency of tertiary amines within a singlecompound of reduced volatility.

SUMMARY

This invention accordingly provides novel compositions for removingcarbon dioxide and acidic sulfide contaminants from fluid streams, forexample, natural gas, synthesis gas, combustion gas, biogas, and otherindustrial fluid streams. Through this disclosure reference to gas orfluid streams is intended to encompass, without limitation, all suchfluids. In a preferred embodiment, the compositions of the invention areused for removal, absorption, or sequestration of CO₂. In otherpreferred embodiments, the compositions are used for removal of otheracidic contaminants, including, without limitation, acidic and sulfidecontaminants, such as CO₂, H₂S, RSH, CS₂, COS, and SO₂.

In an aspect, the invention is an absorbent liquid composition forabsorbing acidic contaminants from fluid streams in an industrialprocess. The composition includes at least one absorbent componenthaving the following general formula (1).

R₁ is H, alkyl, aminoalkyl, or structure (2). Preferably, if R₁ is H,then at least one of R₂, R₃, R₄, or R₅ is not H, and if R₁ is structure(2), then at least one of R₂, R₃, R₄, R₅, R₆, R₇, R₈, or R₉ is not H.R₂, R₃, R₄, R₅, R₆, R₇, R₈, and R₉ are independently H, alkyl, oraminoalkyl, and each m, n, and o are independently 0, 1, or 2 and p andq are independently 0, 1, 2, 3, or 4.

Preferably, the following compounds are excluded from general formula(1): 1,4-bis(2-aminopropyl)piperazine,1,4-bis(3-amino-2,2-dimethylpropyl)piperazine,1,4-bis(3-aminobutyl)piperazine, andN-(2-dimethylaminoethyl)-N′-methylpiperazine.

In another aspect, the invention is an absorbent liquid composition forabsorbing acidic contaminants from fluid streams in an industrialprocess. The composition includes at least one absorbent componenthaving the following general formula (3).

R₁ is H, alkyl, or structure (2). Preferably, if R₁ is H, then at leastone of R₂, R₃, R₄, R₅, R₁₀, or R₁₁ is not H, and if R₁ is structure (2),then at least one of R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, or R₁₁ is notH. R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, and R₁₁ are independently H,alkyl, or aminoalkyl; each m, n, and o are independently 0, 1, or 2; andk is an integer from 2 to 6.

In another aspect, the invention is a process for reducing acidiccontaminants in an industrial fluid stream. The process includescontacting the fluid stream with the described composition to form awashed fluid stream and a rich acid gas scrubbing liquid. At least aportion of the composition including at least a portion of the describedabsorbent component(s) is regenerated from the rich acid gas scrubbingliquid.

It is an advantage of the invention to provide a novel compositionhaving a specific molecular structure that offers reduced volatility anda working capacity for acidic contaminants greater than commonly usedalkanolamine solvents in both low and high-pressure environments.

It is another advantage of the invention to provide a novel compositionthat reduces acidic contaminants in natural, synthesis, and flue gasesand has an increased liquid capacity for acidic contaminants at low gaspressure.

An additional advantage of the invention is to provide a novelcomposition that reduces acidic contaminants in natural, synthesis, andflue gases and has reduced energy of regeneration.

Another advantage of the invention is to provide a novel compositionthat reduces acidic contaminants in natural, synthesis, and flue gasesand has increased depth of removal.

It is a further advantage of the invention to provide a novelcomposition that reduces acidic contaminants in natural, synthesis, andflue gases and has improved stability in the process compared to currentsolvents.

It is yet another advantage of the invention to provide a novelcomposition that reduces acidic contaminants in natural, synthesis, andflue gases and has a higher boiling point resulting in minimized lossesfrom the process and reduced corrosivity.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description, Examples, andFigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a simplified process diagram demonstrating theconfiguration of the equipment in a typical amine solvent wash system.

FIG. 2 shows the common commercially available CO₂ absorbents used forthe comparative testing discussed in Example 1.

DETAILED DESCRIPTION

The following definitions are intended to be clarifying and are notintended to be limiting.

“Alkyl” refers to a monovalent group derived from a straight or branchedchain saturated hydrocarbon by the removal of a single hydrogen atom.Representative alkyl groups include methyl; ethyl; n- and iso-propyl;n-, sec-, iso-, and tert-butyl; C₅ to C₁₂ groups; eicosanyl (C₂₀);heneicosanyl (C₂₁); docosyl (behenyl, C₂₂); tricosanyl (C₂₃);tetracosanyl (C₂₄); pentacosyl (C₂₅), 3-, 7-, and 13-methylhexadecanyl;and the like. Preferred alkyls include methyl, ethyl, propyl, isopropyl,butyl, and isobutyl.

“Aliphatic amine” and/or “aminoalkyl” refers to an alkyl group havingone or more amino substitutions or an amino group having multiple alkylsubstitutions. Representative aminoalkyls include aminomethyl,dimethylaminomethyl, diethylaminomethyl, 2-aminoethyl,2-dimethylaminoethyl, 2-ethylaminoethyl, and the like.

“Amino” or “amine” refers to a group having the structure —NR′R″,wherein R′ and R″ are independently selected from H and alkyl, aspreviously defined. Additionally, R′ and R″ taken together mayoptionally be —(CH₂)_(k)— where k is an integer of from 2 to 6.Representative amino groups include, amino (—NH₂), methylamino,ethylamino, n- and iso-propylamino, dimethylamino, methylethylamino,piperidino, and the like.

“Depth of removal” refers to the amount of CO₂ that escapes theabsorbent solution during peak performance (i.e., CO₂ slip), and is anapproximation of the efficiency of CO₂ absorption.

“Heterocyclic amine” refers to a substituted carbocyclic structurecontaining at least one nitrogen member in the ring.

“Working capacity” refers to the difference between rich loading andlean loading.

This invention has application in a wide array of industrial processesincluding gas fields (e.g., marginal, stranded, and sour gas fields),liquefied natural gas (LNG) liquefaction developments, gas-to-liquids(GTL) developments, synthesis gas, and for the removal of CO₂ fromcombustion gases. The disclosed composition may be used in anyindustrial process, such as single or multi-injection, known in the artor in any specialized high-pressure processes, such as those describedin U.S. Pat. Nos. 6,497,852, “Carbon Dioxide Recovery at High Pressure”and 7,481,988, “Method for Obtaining a High Pressure Acid Gas Stream byRemoval of the Acid Gases from a Fluid Stream,” and in PCT patentapplication no. WO2007077323A1, “Method for Deacidifying a Gas with aFractionally-Regenerated Absorbent Solution with Control of the WaterContent of the Solution.”

Referring to FIG. 1, an exemplary production process (typically found innatural gas processing) where this invention has utility is shown.Production process 100 includes raw gas inlet 105 where gas is contactedcounter currently (typically at pressures greater than atmospheric) witha lean solvent solution (i.e., containing very low concentrations ofacidic contaminants) in absorber column 110. The rich solvent solution(i.e., containing high concentrations of acidic contaminant(s) absorbedfrom the feed gas) drains out of absorber column 110 and passes via apressure reduction valve (not shown) to rich amine flash drum 115 whereco-absorbed volatile hydrocarbons and a portion of the absorbed acid gascontaminate is flashed from the solvent and removed into a vapordischarge stream from the drum.

Treated gas outlet 120 contains gas exiting the top of absorber column110, treated and freed of acid gas contaminant(s). The rich aminesolvent exits rich amine flash drum 115 and proceeds through rich/leanamine exchanger 125, where it is heated, and then into the top ofregenerator column 130, where the acid gas contaminant(s) is separatedfrom the rich solution at low pressure and high temperature as thesolvent flows down the column. The rich solvent is stripped in thecolumn by a countercurrent steam flow produced in amine reboiler 135 atthe base of the column. The hot regenerated solvent accumulates at thebase of the column and the stripped contaminant(s) gasses exit the topof the column with the stripping steam.

Steam and solvent vapor exiting the top of regenerator column 130 entersacid gas condenser 140. Resulting liquids are collected in reflux drum145 for circulation back to the top of the regenerator column throughreflux circulation pump 165. The regenerated hot lean solvent is pumpedfrom the base of regenerator column 130 via rich/lean exchanger 125(through lean amine circulation pump 160) and lean amine cooler 150 backinto the top of absorber column 110 (through lean amine pressure pump170), where the cycle is repeated. Filtration of lean solvent at leanamine filter 155 keeps it clear of solids and contaminants includingdegradation products caused by adverse components of the raw feed gasstream. It should be appreciated that filtration could take place anmultiple and various locations in the process.

In one embodiment, the composition of this invention includes at leastone substituted cyclic diamine component (as shown in structure (1)above). In a preferred embodiment, the composition of this inventionincludes substituted piperazine moieties with substitution at the 1and/or 4 nitrogen positions of the piperazine ring. In otherembodiments, the composition includes substituted cyclic diamines havinga 4- to 12-membered ring.

Exemplary structures of typical mono- or bi-substituted piperazines ofthe invention are shown as structure (4) below, where R₁ is H, alkyl,aminoalkyl, or structure (5) and R is structure (6) shown below.

R₂, R₃, R₄, R₅, R₆, R₇, R₈, and R₉ are independently H, alkyl, oraminoalkyl, and each m, n, and o is independently 0, 1, or 2. In apreferred embodiment, if R₁ is H at least one of R₆, R₇, R₈, or R₉ isnot H, and if R₁ is structure (5) at least one of R₂, R₃, R₄, R₅, R₆,R₇, R₈, or R₉ is not H.

Preferably, the following compounds are excluded:1,4-bis(2-aminopropyl)piperazine, 1,4-bis(3-amino-2,2-dimethylpropyl)piperazine, 1,4-bis(3-aminobutyl)piperazine,and N-(2-dimethylaminoethyl)-N′-methylpiperazine.

In additional embodiments, the composition of the invention includes abisubstituted aminopiperazine, which may be symmetric or asymmetric. Thesubstitutions are typically primary linear amines, such as ethylamine orpropylamine; secondary linear amines, such as N-methyl-ethylamine;branched amines, such as 2-aminopropyl, 2-aminobutyl, and 3-aminobutyl;and linear alkyl groups. In a preferred embodiment, R₁ is a linear amineand R is a branched amine. It should be appreciated that although thesymmetrical structures are proficient CO₂ absorbents, significantadvantages exist in utilizing the asymmetrical variants (i.e., where oneof the substituents is a branched amine and the other is a linear amineor linear alkane).

Structure (7) below illustrates a representative structure for thebisubstituted piperazine embodiment of the invention. R₂, R₃, R₄, R₅,R₆, R₇, R₈, and R₉ are independently H, alkyl, or aminoalkyl. Preferredalkyls include methyl, ethyl, propyl, isopropyl, butyl, and isobutyl.Preferred aminoalkyls include 2-aminopropyl, 2-aminobutyl, aminoethyl,and aminopropyl. In a preferred embodiment, at least one of R₂, R₃, R₄,R₅, R₆, R₇, R₈, or R₉ is not H. The value of each m, n, and o areindependently 0, 1, or 2.

Representative monosubstituted piperazines include2-aminopropyl-piperazine, 2-aminobutyl-piperazine, 1-acetylpiperazine,and l-formylpiperazine. Representative examples of typical bisubstitutedpiperazines include 1,4-bis-(2-aminobutyl)-piperazine;1,4-bis-(N-methyl-aminoethyl)-piperazine;1-(2-aminobutyl)-4-methylpiperazine;1-(2-aminopropyl)-4-methylpiperazine; and1-(2-aminopropyl)-4-ethylpiperazine;1-aminoethyl-4-(2-aminobutyl)-piperazine;1-aminoethyl-4-(2-aminopropyl)-piperazine;1-aminopropyl-4-(3-aminobutyl)-piperazine;1-aminoethyl-4-(N-methyl-aminoethyl)-piperazine; and the like.

In yet another embodiment, the composition of the invention includes alinear or branched polyamine Structure (8) illustrates a representativestructure for this embodiment.

In an embodiment, R₁ is H, alkyl, or structure (9). Preferably, if R₁ isH and at least one of R₂, R₃, R₄, R₅, R₁₀, or R₁₁ is not H, and if R₁ isstructure (9), then at least one of R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀,or R₁₁ is not H.

In another embodiment, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, and R₁₁ areindependently H, alkyl, or aminoalkyl. Preferred alkyls are methyl,ethyl, propyl, isopropyl, butyl, and isobutyl. Preferred aminoalkyls are2-aminopropyl, 2-aminobutyl, aminoethyl, and aminopropyl. Each m, n, ando are independently 0, 1, or 2 and k is an integer from 2 to 6.Preferably, k is from 2 to 4.

In one embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (I).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (II).

In an additional embodiment, the composition of the invention includesan absorbent component of the formula illustrated in structure (III).

In yet another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (IV).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (V).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (VI).

In a further embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (VII).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (VIII).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (IX).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (X).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XI).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XII).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XIII).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XIV).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XV).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XVI).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XVII).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XVIII).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XIX).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XX).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XXI).

In another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XXII).

In yet another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XXIII).

In yet another embodiment, the composition of the invention includes anabsorbent component of the formula illustrated in structure (XXIV).

The composition of the invention may also include derivatives and/orsalts of the disclosed structures. Representative derivatives includecarbonates, bicarbonates, carbamates, ureas, and amides. Representativesalts include all inorganic, mineral, and organic salts.

It is the intent of this invention to use the disclosed structures in amultitude of compositions including single or multiple componentsolutions in water or as combined with other acid gas solvent componentssuch as tetramethylene sulfone (i.e., Sulfolane), MDEA, DEA, MEA, andthe like in water and/or other mutual solvents.

For example, single and multiple component solutions range from about0.01 to about 100 wt % actives or from about 1 to about 75 wt % activesand include the use of solvents, such as water, alcohols, polyols, otheracid gas solvents, and organic solvents. In a preferred embodiment, thecomposition includes about 10 to about 75 wt % or from about 40 to about50 wt % actives. Additionally, the composition generally includes anamount of solvent in the range of 0 to 99.09 wt %, depending upon theamount of actives.

The scrubbing liquid used in the composition of the invention may alsoinclude, for example, one or more of the following components:aminoethyl-piperazine; 2-aminoethyl-piperazine;2-aminopropyl-piperazine; 2-aminobutyl-piperazine; 1-acetylpiperazine;1-formylpiperazine; 1,4-bis-aminoethyl-piperazine;1,4-bis-aminopropyl-piperazine; 1,4-bisaminobutyl-piperazine;1,4-bis-(2-aminopropyl)-piperazine; 1,4-bis-(2-aminobutyl)-piperazine;1,4-bis-(N-methyl-aminoethyl)-piperazine;1-(2-aminobutyl)-4-methylpiperazine;1-(2-aminopropyl)-4-methylpiperazine;1-(2-aminopropyl)-4-ethylpiperazine;1-aminoethyl-4-(2-aminobutyl)-piperazine;1-aminoethyl-4-(2-aminopropyl)-piperazine;1-aminoethyl-4-(N-methyl-aminoethyl)-piperazine; 2-morpholinoethanamine;2-aminopropyl-morpholine; 2-(1H-imidazol-1-yl)ethanamine;2-aminopropyl-piperidine; 2-aminopropyl-pyrrolidine;N1-(2-aminopropyl)butane-1,4-diamine;N1-(3-aminopropyl)propane-1,2-diamine; water; sulfolane,N-methylpyrrolidone;

-   N-alkylated pyrrolidones, piperidones and morpholines corresponding    to the foregoing; methanol; mixtures of dialkyl ethers of    polyethylene glycols; C₁ to C₄ dialkylether monoethylene glycols; C₁    to C₄ monoether monoethylene glycols; C₁ to C₄ dialkylether poly    ethylene glycols; C₁ to C₄ monoether polyethylene ethylene glycols;    C₁ to C₄; ethylene glycol; diethylene glycol; triethylene glycol;    N,N-dimethyl formamide; N-acetyl morpholine; N-formyl morpholine;    N,N-dimethyl imidazolidin-2-one; N-methyl imidazole; and the like.

In another embodiment, the composition of the invention may also includeother components. Representative other components include blends ofamines, activators, antifoaming agents, co-absorbents, corrosioninhibitors, solvents, coloring agents, the like, and combinationsthereof. Representative examples include alkanolamines;cyclotetramethylene sulfone and its derivatives; aliphatic acid aminessuch as acetyl morpholine or N-formyl morpholine; alkali metal compoundswhich provide alkaline hydrolysis products, such as alkali metalhydrolysis and hydrocarbonates; aliphatic and cycloaliphatic mono- anddiamines, such as triethylene diamine, dicyclohexyl amine,N-ethyl-cyclohexylamine, and N,N-diemthylcyclohexylamine; the like; andcombinations thereof.

In another embodiment, coabsorbents include one or more componentsselected from calcium oxide, calcium lignosulfonate, calcium silicatehydrates, calcium hydroxide, calcium carbonate, calcium bicarbonate,sodium carbonate, sodium bicarbonate, trona, sodium sesquicarbonate,soda ash, nacholite, sodium aluminate, metal oxides, and the like.

Activators and coabsorbents are preferably present in the composition ofthe invention from about 0.01 to about 90 wt %, more preferably fromabout 1 to about 50 wt %, and most preferably from about 1 to about 25wt % (wt % based on the weight of total actives).

In a further embodiment, the invention is a process for reducing acidiccontaminants in an industrial fluid stream. The fluid stream iscontacted with the disclosed composition to form a washed fluid streamand a rich acid gas scrubbing liquid. Typically, the composition iscontacted with the gas stream at a temperature ranging from about 0 toabout 200° C. In certain cases, this temperature range may be from about0 to about 100° C. or from about 20 to about 65° C. Industrial processesgenerally run at a pressure ranging from about 0 to about 200 atm, fromabout 0 to about 100 atm, from about 0 to about 70 atm, from about 0 toabout 50 atm, from about 0 to about 25 atm, from about 0 to about 10atm, or from about 1 to about 5 atm during the time when the compositionis contacted with the fluid stream. U.S. Pat. No. 4,556, “Bis TertiaryAmino Alkyl Derivatives as Solvents for Acid Gas Removal from GasStreams” discloses pressure ranges from 4 to 70 atm. Canadian patentapplication no. 2,651,888, “Carbon Dioxide Absorbent Requiring LessRegeneration Energy” discloses pressures from 1 to 120 atm. It should beappreciated that this invention is operable in any of these or otherpressure ranges encountered in the relevant art.

The rich acid gas scrubbing liquid is further processed through aregeneration system where at least a portion of the compositionincluding at least a portion of the absorbent compound(s) contacted withthe fluid stream are regenerated. The regeneration step normally takesplace at a higher temperature than absorption (depending on theparticular industrial process), usually at a temperature ranging fromabout 0 to about 500° C., from about 20 to about 250° C., or from about50 to about 150° C. The pressure range for the regeneration step isnormally from about 0 to about 10 atm or from about 1 to about 5 atm. Incertain cases, the regeneration step may be carried out via asteam-assisted reboiler. Regeneration may also be carried out via afractional regeneration process (e.g., WO 2007/077323, “Method forDeacidifying a Gas with a Fractionally-Regenerated Absorbent Solutionwith Control of the Water Content of the Solution”).

The foregoing may be better understood by reference to the followingexamples, which are intended for illustrative purposes and are notintended to limit the scope of the invention.

Example 1

The testing in this Example was used as a means of screening potentialacidic contaminant scavengers and also to confirm the performance ofexisting commercially available scavengers. The test was designed todetermine the maximum capacity of an amine solvent in absorbing acidicgases. Different amine solvents were compared. The amine solvents weresaturated with acidic gases at a constant pressure and temperature untilno more gas was able to be absorbed. The difference between the rich andlean loadings was used to determine the working capacity. The test wasdesigned to regenerate the solvent by boiling to remove the acidic gasesso that the lean loading of CO₂ in an amine solvent could be determined.

Solvent performance was characterized by liquid loading at equilibriumwith defined composition gas mixtures at simulated amine contactor andregenerator conditions relative to industry benchmarks.

To highlight the advantages of the disclosed novel amines, severalspecific samples were benchmarked against common commercial CO₂absorbents (such as methyldiethanolamine (MDEA), 33.8/6.2methyldiethanolamine/piperazine (DMDEA), diglycolamine (DGA),monoethanolamine (MEA), aminoethyl-piperazine (AEP), andbisaminopropylpiperazine (BAPP), illustrated in FIG. 2) using alaboratory-scale fixed bed absorption cell and a batch reboiler. The“Sorbent” numbers indicated in Table 1 correspond to the structurenumbers above. The equilibrium saturation test to determine the richloading (weight % CO2 absorbed by fresh sorbent) was run by exposing anaqueous solution of the absorbent at 40° C. to 30 psi of CO₂ untilsaturation was reached. The lean loading (weight % CO₂ remainingassociated with the absorbent after regeneration) was determined byrefluxing the aqueous solution of the absorbents for two hours atatmospheric pressure. The working capacity is defined as the richloading minus the lean loading. It is the working capacity that mostaccurately reflects the capacity of the chemical to absorb CO₂ underprocess conditions. The results of this evaluation are reported in Table1.

To determine rich loading, the equipment consisted of a high pressuregas panel that was capable of receiving supplies of 100% CO₂, CO₂/N₂mixtures and CO₂/H₂S/N₂ mixtures. The chosen gas was fed via a mass flowcontroller (Sierra series 100 mass flow controller, available fromSierra Instruments, Inc. in Monterey, Calif.) to the reaction vessel. Agas totalizer (a Sierra Compod) attached to the mass flow controllermeasured the volume of gas used.

Once the appropriate gas cylinder valve and regulators were opened, therecirculating bath was set to a temperature of 40° C. A 200 ml glassreaction vessel was attached to the head of a Buchi Picoclave. The inletand outlet valves to the reaction vessel were closed and the inletpressure regulator was set to 30 psi. The gas mixture was set to 100%CO₂ and the flow rate was set to 0.5 liters/min. After allowing the gaspressure to build to 30 psi at the reactor inlet, the amine solution wasprepared at the concentration indicated in Table 1 and, after beingbrought to the same temperature as the reaction vessel, was added to thereaction vessel and stirred at 1,000 rpm.

The inlet valve was opened and the reactor pressure was allowed toequilibrate to 30 psi. When the pressure in the reactor reached 30 psi,the inlet valve was closed the inlet valve and the gas flow was shutoff. The volume in the reactor vessel was recorded. Gas flow was resumedafter 5 minutes and continued until the pressure equalized to 30 psi.This procedure was repeated until no additional CO₂ was absorbed asmeasured by the final volume. The wt % rich loading of the amine wascalculated from the final volume of CO₂ absorbed.

To determine lean loading, the amine composition to be regenerated waspoured into a 250 ml 3-neck flask equipped with mechanical stirring anda chilled condenser (8° C.). The amine solution was slowly heated to150° C. to help avoid a sudden release of gas which would have causedthe solution to foam. The solution was refluxed for 2 hours and thencooled to room temperature. The lean loading of the amine was determinedvia a standard barium chloride back titration.

To determine depth of removal, a mass flow controller (Sierra series 100mass flow controller) was used to control the flow of gas through thereactor vessel. The chosen gas was fed via the mass flow controller tothe saturation vessel (which contained deionized water) and then intothe reaction vessel. From the reaction vessel, the gas was fed via abackpressure regulator through a Dreschel bottle containing ethyleneglycol and a drying tube containing silica gel to the CO₂ analyzer. TheCO₂ analyzer (Signal 7000FM CO₂ analyzer) recorded the concentration ofCO₂ flowing through it. The recirculating bath was set to the requiredtemperature of 40° C. The 200 ml glass reaction vessel was fitted to thehead of a Buchi Picoclave. A Dreschel bottle containing ethylene glycoland a drying tube containing silica gel was connected to the gas lineprior to the CO₂ analyzer, and the backpressure regulator was set to 90psi. The gas mixture (25% CO₂/75% N₂) and the flow rate (0.45liters/min) were then set and allowed to stabilize for 30 minutes. Theamine solution was prepared at the concentrations indicated in Table 1and heated as above. The amine was then added to the reaction vessel andthe stirrer was set to 1,000 rpm. The downstream regulator was closedand the data recording began. The gas flow was allowed to continue untilequilibrium was reached ˜3 hrs. At the end of the run, the gas flow wasstopped, the inlet valve to the reaction vessel was closed, and the datarecording was stopped.

TABLE 1 NPX Amines vs. Common Absorbents Rich Rich Lean Lean WorkingWorking Depth of Sorbent MW Wt. % (Aq) Loading Mole Ratio Loading MoleRatio Capacity Mole Ratio Removal XXII 145.25 43.5% 17.64% 1.63 1.97%0.15 15.67% 1.41 0.00% XXI 131.21 39.3% 17.54% 1.61 2.21% 0.17 15.33%1.37 NA XIII 157.26 40.0% 13.58% 1.40 0.09% 0.01 13.49% 1.39 0.41% XI186.3 40.0% 13.28% 1.62 0.19% 0.02 13.09% 1.59 0.10% X 200.32 40.0%11.31% 1.45 0.22% 0.03 11.09% 1.42 0.15% VI 157.26 40.0% 12.74% 1.300.04% 0.00 12.70% 1.30 0.18% IV 200.32 40.0% 11.78% 1.52 0.20% 0.0211.58% 1.49 0.24% II 200.32 40.0% 13.27% 1.74 0.06% 0.01 13.21% 1.73 NAI 228.38 40.0% 11.79% 1.73 0.00% 0.00 11.79% 1.73 0.35% MDEA 119.1640.0% 10.88% 0.83 0.00% 0.00 10.88% 0.83 1.63% DMDEA 114.41 40.0% 11.27%0.83 0.03% 0.00 11.24% 0.82 0.35% DGA 105.14 40.0% 9.43% 0.62 0.13% 0.019.30% 0.61 0.11% MEA 61.08 35.0% 13.50% 0.62 1.41% 0.06 12.09% 0.550.00%

The tested amines on average absorbed about 1.5 moles of CO₂ per mole ofabsorbent compared to less than 1 mole of CO₂ per mole of the commonabsorbents. Although not all the tested amines outperformed the commonabsorbents, Sorbents II, VI, XI, XIII, XXI, and XXII showed asignificant increase in working capacity (5 to 30% increase based onMEA). These amines, with the exception of Sorbents XXI and XXII, alsohave a significantly lower lean loading than MEA.

The boiling points of the disclosed amines range from about 200 to about280° C. at 1 atm (compared to MEA at 170° C. and 1 atm). Such higherboiling points help significantly reduce the losses and potentialenvironmental releases currently associated with the volatility of MEAand also help to prevent CO₂ contamination during solvent regeneration.Initial laboratory stability testing has indicated that unlike MEA,which is known to degrade rapidly under process condition, the disclosedamines are highly robust at simulated process conditions showing nosigns of degradation.

To further highlight the utility of the tested amines for carboncapture, a 25% CO₂ gas stream at 90 psi was passed through theabsorbents at 40° C. until they reached saturation and the depth ofremoval was recorded. Importantly, the depth of removal for many of thetested amines approached 0%, an indication that they are highlyefficient at CO₂ capture as shown in Table 1.

Example 2

Although a reduction in the lean loading of branched compounds overlinear compounds would have been expected, the select group of moleculestested showed a unique increase in the working capacity of the branchedtargets (Table 2). The “Sorbent” numbers indicated in Table 2 correspondto the structure numbers above. This unusual reactivity is particularlyevident when comparing the linear BAPP to the branched Sorbent II. Thetwo molecules are identical in molecular weight and were tested underidentical conditions; however, Sorbent II shows a 9.5% increase inworking capacity. This unexpected and surprising increase in capacity isthought to occur via a change in the mechanism by which the amine reactswith CO₂. It has been proposed that the linear amine favors directreaction with the CO₂ to form the carbamate, and the branched aminefavors (similar to tertiary amines) indirect reaction with the CO₂ toform a bicarbonate salt. Thus, the reaction between CO₂ and the branchedamines are of greater efficiency.

TABLE 2 Branched vs. Linear Working Lean Branched/ Wt. % Mole MoleSorbent Linear MW (Aq) Ratio Ratio % Increase XIII Branched 157.2640.00% 1.39 0.01 17.80% VI Branched 157.26 40.00% 1.30 0.00 10.17% AEPLinear 129.20 40.00% 1.18 0.05 0.00% II Branched 200.32 40.00% 1.73 0.019.49% I Branched 228.38 40.00% 1.73 0.00 9.49% BAPP Linear 200.32 40.00%1.58 0.14 0.00% XXII Branched 145.25 43.50% 1.41 0.15 12.80% XXIBranched 131.21 39.30% 1.37 0.17 9.60% DETA Linear 103.17 30.90% 1.250.19 0.00%

Example 3

This Example compared the absorption data of AEP and Sorbents VI andXIII. The testing revealed that alkyl substitution of one of thepiperazine nitrogens with small alkyl groups (such as methyl and ethyl)afforded an unexpected increase in the capacity of the sorbent (Table3). The “Sorbent” numbers indicated in Table 3 correspond to thestructure numbers above. Sorbents VI and XIII showed an increase incapacity over the linear AEP, but unlike Sorbents I and II, which had anequal increase regardless of the length of the alkyl branch (ethyl vs.methyl), Sorbent XIII showed a significant increase in capacity overStructure VI.

TABLE 3 Alkyl Substitution of Piperazine Working Lean Branched/ Wt. %Mole Mole Sorbent Linear MW (Aq) Ratio Ratio % Increase XIII Branched157.26 40.00% 1.39 0.01 17.80% VI Branched 157.26 40.00% 1.30 0.0010.17% AEP Linear 129.20 40.00% 1.18 0.05 0.00%

Example 4

This Example illustrates that absorbents with asymmetrical substitution(e.g., a branched amine and a linear amine) demonstrated reduced depthof removal with little to no penalty in terms of working capacity andlean loading (Table 4). The “Sorbent” numbers indicated in Table 4correspond to the structure numbers above.

TABLE 4 Asymmetrical Substitution Wt. % Working Lean Depth of Sorbent MW(Aq) Mole Ratio Mole Ratio Removal XI 186.3 40.0% 1.59 0.02 0.10% X200.32 40.0% 1.42 0.03 0.15% IV 200.32 40.0% 1.49 0.02 0.24% I 228.3840.0% 1.73 0.00 0.35% BAPP 200.32 40.0% 1.58 0.14 0.16%

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While this invention may be embodied in many differentforms, there are described in detail herein specific preferredembodiments of the invention. The present disclosure is anexemplification of the principles of the invention and is not intendedto limit the invention to the particular embodiments illustrated.

Any ranges given either in absolute terms or in approximate terms areintended to encompass both, and any definitions used herein are intendedto be clarifying and not limiting. Notwithstanding that the numericalranges and parameters setting forth the broad scope of the invention areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical value, however,inherently contains certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.Moreover, all ranges disclosed herein are to be understood to encompassany and all subranges (including all fractional and whole values)subsumed therein.

Furthermore, the invention encompasses any and all possible combinationsof some or all of the various embodiments described herein. Any and allpatents, patent applications, scientific papers, and other referencescited in this application, as well as any references cited therein andparent or continuation patents or patent applications, are herebyincorporated by reference in their entirety. It should also beunderstood that various changes and modifications to the presentlypreferred embodiments described herein will be apparent to those skilledin the art. Such changes and modifications can be made without departingfrom the spirit and scope of the invention and without diminishing itsintended advantages. It is therefore intended that such changes andmodifications be covered by the appended claims.

The claimed invention is:
 1. A scrubbing liquid composition forabsorbing acidic contaminants from fluids in an industrial process, thecomposition comprising: (a) at least one absorbent component having ageneral formula:

or a carbonate, bicarbonate, urea, or amide thereof, or a salt thereof;wherein (i) R₁ is selected from the group consisting of: H, alkyl,aminoalkyl, and the following structure (A),

(ii) R₂, R₃, R₄, R₅, R₆, R₇, R₈, and R₉ are independently H, alkyl, oraminoalkyl; wherein if R₁ is H at least one of R₂, R₃, R₄, or R₅ is notH, and if R₁ is the structure (A) at least one of R₂, R₃, R₄, R₅, R₆,R₇, R₈, or R₉ is not H, (iii) each m, n, and o is independently 0, 1, or2, and (iv) p and q are independently 0, 1, 2, 3, or 4, with the provisothat the following compounds are excluded:1,4-bis(2-aminopropyl)piperazine,1,4-bis(3-amino-2,2-dimethylpropyl)piperazine,1,4-bis(3-aminobutyl)piperazine, andN-(2-dimethylaminoethyl)-N′-methylpiperazine; and (b) a solvent.
 2. Thecomposition of claim 1, wherein the alkyl for R₁ to R₉ is independentlyselected from the group consisting of: methyl, ethyl, propyl, isopropyl,butyl, and isobutyl.
 3. The composition of claim 1, wherein theaminoalkyl for R₁ to R₉ is selected from the group consisting of:2-aminopropyl, 2-aminobutyl, aminoethyl, and aminopropyl.
 4. Thecomposition of claim 1, wherein said absorbent component is selectedfrom the group consisting of: (I), (III), (IV), (V), (VI), andcombinations thereof


5. The composition of claim 1, wherein said absorbent component isselected from the group consisting of: (VII), (VIII), (X), (XI), (XII),and combinations thereof


6. The composition of claim 1, wherein said absorbent component isselected from the group consisting of: (XIII), (XIV), (XV), (XVI),(XVII), (XVIII), (XIX), (XX), and combinations thereof.


7. The composition of claim 1, wherein the acidic contaminant isselected from the group consisting of: CO₂, H₂S, RSH, CS₂, COS, SO₂, andcombinations thereof.
 8. The composition of claim 1, wherein saidabsorbent compound is present in an amount ranging from about 0.01 toabout 100 wt %.
 9. The composition of claim 1, further comprising one ormore components selected from the group consisting of: amines,activators, antifoaming agents, co-absorbents, corrosion inhibitors,coloring agents, and combinations thereof.
 10. The composition of claim1, wherein the solvent is selected from the group consisting of: water,alcohols, polyols, other acid gas solvents, organic solvents, andcombinations thereof.
 11. The composition of claim 1, wherein (i) R₁ isH, (ii) R₂, R₃, R₄, and R₅ are independently H, alkyl, or aminoalkyl;wherein at least one of R₂, R₃, R₄, or R₅ is not H, (iii) each m, n, ando is independently 0, 1, or 2, and (iv) p and q are independently 0, 1,2, 3, or
 4. 12. The composition of claim 11, wherein said absorbentcomponent is selected from the group consisting of: (V), (VI), (VII),and combinations thereof


13. The composition of claim 1, wherein (i) R₁ is the followingstructure (A),

(ii) R₂, R₃, R₄, R₅, R₈, and R₉ are independently H, alkyl, oraminoalkyl; wherein at least one of R₂, R₃, R₄, R₅, R₈, and R₉ is not H,(iii) R₆, and R₇ are independently H, (iv) each m, n, and o isindependently 0, 1, or 2, and (v) p and q are independently 0, 1, 2, 3,or
 4. 14. The composition of claim 13, wherein said absorbent componentis selected from the group consisting of: (III), (IV), (VIII), (X),(XI), (XVII), (XIX), (XX), and combinations thereof


15. The composition of claim 14, wherein said absorbent component is(XI).
 16. The composition of claim 1, wherein (i) R₁ is the followingstructure (A),

(ii) R₂, R₃, R₄, R₅, R₇, R₈, and R₉ are independently H, alkyl, oraminoalkyl, (iii) R₆ is independently ethyl, propyl, isopropyl, butyl,or isobutyl, (iv) each m, and n are independently 0, 1, or 2, (v) o is 1or 2, and (vi) p and q are independently 0, 1, 2, 3, or
 4. 17. Thecomposition of claim 16, wherein said absorbent component is (I).


18. A scrubbing liquid composition for absorbing acidic contaminantsfrom fluids in an industrial process, the composition comprising: (a) atleast one absorbent component selected from the group consisting of (I),(IV), (V), (VI), (XI), and combinations thereof:

and (b) a solvent.
 19. The composition of claim 18, wherein theabsorbent component is (XI).